SAN SALVADOR — Luz Janet Alfaro, a 23-year-old human rights activist, had been in police custody 10 days before she appeared on national television to announce that she was a guerrilla defector.

Alfaro asserted that the Human Rights Commission, a non-government agency where she had worked since 1982, was run by Farabundo Marti National Liberation Front guerrillas, as were three Mothers Committees for Political Prisoners and the Disappeared and other groups that represent those missing, detained and displaced during six years of civil war in El Salvador.

In that press conference May 30 and subsequent interviews, Alfaro charged that the Roman Catholic, Lutheran and Baptist churches were infiltrated by rebels, who were siphoning off thousands of dollars in international aid to the armed guerrilla groups.

Dozens Identified

She named dozens of human rights and refugee workers, lawyers and religious leaders who, she said, are members of leftist guerrilla groups fighting to overthrow the U.S.-backed government.

The sweeping charges, reproduced by the government in newspaper ads, have sent waves of fear through religious and human rights workers, some of whom charge that the government has embarked on a campaign to brand all humanitarian work as subversive.

Since the war began in 1980, thousands of Salvadorans have been killed or have disappeared for political reasons, including priests, lay religion instructors, union and student leaders and human rights workers. Many of the hundreds of killings each month were carried out by right-wing death squads, and the bodies often were dumped in public places as a warning to others.

Violence Level Lower

Today, the level of the violence is lower than it was in the early 1980s, and increasing numbers of people are arrested rather than killed for alleged subversive activities. But some political killings still occur each month, and in the jails, physical or psychological torture is commonly practiced on political prisoners, according to human rights workers, and a vast majority of the nearly 1,000 political prisoners have not received a hearing or trial.

"So many people were threatened in the past that you don't need to do a lot in the present to shake them up," a human rights worker said.

After Alfaro was seized, nine other human rights activists were detained and seven of them were jailed. Alfaro's sister, Syonara, who was a member of the Human Rights Commission, and Dora Angelica Campos, a secretary for the Bishop Oscar Arnulfo Romero Mothers Committee, say they also were members of Farabundo Marti organizations and publicly allege that human rights groups where they worked were infiltrated by rebels. They, like Alfaro, are not now detained.

Defectors' Spokeswoman

Alfaro has been the leading spokeswoman among the proclaimed defectors and has given detailed accounts of her work and of the guerrillas' political organization to Americas Watch, a U.S.-based human rights group, and to reporters.

It is virtually impossible to determine which of Alfaro's myriad public allegations might be true, because no evidence has been presented. Sources who closely follow the Farabundo Marti Front's political work say it is likely the guerrillas tried to infiltrate groups such as the Human Rights Commission, but they see no proof linking them to the churches.

In early years of the war, journalists sometimes made contact with guerrillas through the Human Rights Commission.

Alfaro's declarations have led to speculation that she was a government plant in the commission, a defector-turned-spy, or a disgruntled rebel embittered by infighting. She describes deep divisions within the human rights groups among what she says were members of different factions of the Farabundo Marti Front.

'Inappropriate Substitute'

Americas Watch has called the government-organized press appearances and the defectors' public charges against others "an inappropriate substitute for judicial proceedings." An American Embassy official admitted "concern" for the people Alfaro called guerrillas, most of whom have not been detained. Those so named have denied her charges.

Some human rights workers say Alfaro and her accusations are part of a counterinsurgency campaign to discredit ecumenical and refugee work that does not always dovetail with government policies or military strategy.

Since last year, the army and police have made it a frequent practice to present captured rebels or rebel collaborators to the press as part of their "psychological operations" to discourage cooperation with guerrillas and to win public support.

But the propaganda value has been mixed for the government. While guerrilla defector Miguel Castellanos has enthusiastically urged his comrades to put down their arms, other prisoners, including three suspects in last year's guerrilla attack on two outdoor cafes that left four U.S. Marines and nine others dead, have appeared to be less than willing showmen when paraded in public.